Unwanted plants, such as weeds, reduce the amount of resources available to crop plants and can have a negative effect on crop plant yield. Commonly unwanted plants in crop plant environments include broadleaf plants and grasses.
Herbicides are used to kill unwanted plants, such as weeds, in crop plant environments. Herbicides are expensive, and their use may result in unintentional consequences such as groundwater contamination, environmental damage, herbicide-resistant weeds, and human and mammalian health concerns. It is therefore desirable to minimize the amount of herbicides applied to a crop-growing environment or any area in need of weed control.
Unwanted plants, such as weeds, may greatly reduce yields of crop plants. For example, a Horseweed infestation reportedly was responsible for an 80% reduction in soybean yields. Bruce, J. A., and J. J. Kells, Horseweed (Conyza Canadensis) control in no-tillage soybeans (Glycine max) with preplant and preemergence herbcides, Weed Technol. 4:642-647 (1990). Therefore, controlling weeds, and especially grasses and Horseweed, is a major concern of crop growers.
Further, Horseweed and other grasses are becoming resistant to the widely used herbicide glyphosate. As early as 2000, glyphosate resistant Horseweed was reported in Delaware. Glyphosate resistant Horseweed has since been reported in numerous states. Accordingly, there is a need for new products that can provide effective kill rates of glyphosate resistant Horseweed.
Weeds are also becoming resistant to herbicides that inhibit acetolactate synthase (ALS) and protoporphyrinogen oxidase (PPO). Horseweed has also been reported to be resistant to 2,4-D and dicamba. Accordingly, there is a need for new technology to control weeds that are resistant to commercially available herbicides.
In most fields throughout the Midwest and Mid-South, in-crop burndown applications are the only options for controlling Horseweed due to weather and timeliness of applications. Repeated applications of these chemistries have contributed to expanding resistance and lack of control. Repeated applications of single effective active ingredients will only continue to select for resistant populations of weeds, thus leaving no alternatives for weed control other than mechanical. Mechanical removal of weeds requires extensive use of resources and is not an option for no-till or highly erodible land.
No-till farming has been increasing in popularity because it has many benefits, including decreased labor time and decreased soil erosion. However, one of the downsides of no-till farming is that weeds are harder to control in these areas because they are not subjected to tilling. Accordingly, there is an increasing need for alternative ways to handle weed infestation.
Pyroxasulfone (3-[[[5-(difluoromethoxy)-1-methyl-3 (trifluoromethyl)-1H-pyrazol-4-yl]methyl]sulfonyl]-4,5-dihydro-5,5-dimethylisoxazole) is an herbicide that has residual weed control. Pyroxasulfone, however, does not have post emergence weed control. Pyroxasulfone is commercially available in a mixture with flumioxazin (Fierce®, available from Valent U.S.A. Corporation).
Glufosinate (DL-4-[hydroxy](methyl)phosphinoyl]-DL-homoalaninate) and its salts such as DL-glufosinate-ammonium are known to have herbicidal activity and are commercially available, e.g. Basta™ and Liberty™ (available from Bayer CropSciences). Glufosinate is a phosphinic acid that inhibits the activity of glutamine synthetase which results in ammonium accumulation in the plants. The ammonia destroys the cells which inhibits photosynthesis. Bialaphos is another glutamine synthesis inhibitor that is naturally produced by a soil microorganism.
When applied alone, glufosinate often yields unsatisfactory weed control. Several applications and/or high dosage rates are required for high efficacy. Further, glufosinate has little effect of some broadleaf species and rhizomatous grasses. In an effort to overcome these shortcomings, glufosinate is frequently applied with at least one additional herbicide, such as 2,4-D, dicamba, triazines such as atrazine or metribuzin, chloroacetanilides such as metholachloror dimethenamid (including dimethenamid-P), linuron and/or pendimethalin. However, the effectiveness of such combinations is often not satisfactory and high application rates are still required to achieve acceptable control of grass weeds and broadleaves. Moreover, the reliability of such combinations depends strongly on the weathering conditions and certain difficult to control weed species may escape. In addition, the herbicidal activity of these compositions persists only for a short time, which allows effective burndown only within a small timeframe prior to planting a crop. Moreover, the persistence of the herbicidal activity strongly depends upon the weathering conditions.
U.S. Patent Application Publication No. 2011/0065579 discloses thousands of mixtures of herbicides, one of which is a mixture of glufosinate and pyroxasulfone in a ratio range of from 2000:1 to 1:10. However, this publication fails to provide guidance within this broad range of acceptable amounts of glufosinate or pyroxasulfone. Further, this publication does not teach or suggest narrower ratios that would produce acceptable results. In addition, this publication fails to suggest the synergy that Applicants discovered between glutamine synthesis inhibitors and pyroxasulfone.
In summary, there is a need for a composition that reduces the amount of herbicides necessary to obtain sufficient weed control while minimizing the harm to crop plants. As more weeds become resistant to herbicides, alternative compositions with high weed control are desired. Further, as no-till farming continues to increase in popularity, there is a greater need for effective herbicides. A composition with effective weed control and lower dosage rate will lead to increased crop plant yields, and decreased environmental, human, and mammalian health concerns.